Previously, many granular products and some liquids have been shipped and stored in large bulk bags which may contain as much as a ton or more of material. Some of these bags are flexible and when emptied can be folded to a generally flat condition. Examples of such flexible bags are disclosed and claimed in U.S. Pat. Nos. 4,596,040, 4,781,472, 4,781,475, 4,790,029, 4,798,572, 5,087,235, 5,104,236, and 5,127,893.
These flexible bags have generally rectangular sidewalls and a substantially flat top wall so that when filled the bags can be stacked one on top of another. For some applications, the bags are made of a woven fabric and for other applications, a plastic material. For some uses, and particularly for storing liquids, a bag or liner of a water impervious plastic material is received in and reinforced and protected by a bag of a woven fabric. Usually, these bags have a spout in one or both of ends for filling and emptying the bag.
A prior known bag, disclosed in U.S. Pat. No. 4,953,987, has a truncated cone-shaped top wall to facilitate filling and an iris-type closure in the top wall for tightening the top and sidewalls of the bag around bulk material within the bag to produce a bulk bag which can support another bag vertically stacked. The cone-shaped top wall is attached to the top edges of four sidewalls which are connected to each other at their side edges. The bag construction disclosed also has a bottom wall connected to the bottom edges of the sidewalls and an inlet spout attached adjacent the truncated portion of the top wall.
The iris-type closure is constructed of a cord received in an annular channel in the top wall. In use, the cord is tightened to inwardly constrict the top wall fabric around the truncated portion to flatten the top wall tightly against the bulk material within the bag. As the closure is tightened, excess bag fabric is gathered, preventing the formation of loose pockets of sidewall fabric which makes the bag more stable for receiving another bag stacked on top. Unfortunately, a bag of this construction must be substantially completely filled for the closure to gather enough top wall fabric to effectively tighten the bag around the bulk material. Should the bag be incompletely filled or improperly leveled, loose pockets of sidewall fabric still may form which can cause the bag to slump, buckle or topple possibly damaging or spilling the contents of the bag or another bag vertically stacked.
Another problem with this bag construction is that adjacent sidewall panels are connected along side edges which can lead to premature bag failure. Any weakness in any line of connection between panels can cause the bag to rupture when another bag is placed on top. Similarly, should the bag, when supporting another bag on its top, slump or bulge because it was incompletely filled, the resultant uneven distribution of stress in the sidewall panels can cause the underlying bag to burst along one of its side edges.